Spherical Particles of Zirconia-Titania of Hexagonal Structure from a Neutral Amine Route

Through the sol–gel process, using the so-called neutral amine route, spherical particles of 1:1 zirconia–titania were synthesized from zirconium(IV) and titanium(IV) butoxides as well as 1,12-diaminododecane as precursor species. The obtained product exhibited a hexagonal structure, as determinated by X-ray diffraction data. The obtained material was also characterized by thermogravimetry, differential scanning calorimetry, infrared spectroscopy, scanning electron microscopy, and surface area measurements. Despite the release of template molecules on heating, the spherical morphology was retained up to about 1200°C, at which the disruption of the spheres took place.     

Effects of Adsorbed Polyaniline on Redox Process on MoO3 Surface

The effects exhibited by adsorbed conducting polyaniline on the redox process on a molybdenum oxide surface were studied. Thermogravimetric results indicate a 4% polyaniline deposition. Cyclic voltammograms of the adsorbed polymer on MoO3 show that polyaniline exerts remarkable effects on the molybdenum blue oxidation-reduction process, with oxidation and reduction potentials of 0.33 and 0.18 V, respectively. This effect strongly enhances the electrode response, and can be used as an important tool in qualitative and/or quantitative determinations of molybdenum in solution as well as in any substrate. Copyright 1999 Academic Press.     

Kinetics of disassembly of a DNA-bound porphyrin supramolecular array

trans-Bis(N-methylpyridinium-4-yl)diphenylporphine forms extended, organized assemblies on DNA templates under appropriate conditions of concentration, ionic strength, and temperature. Addition of beta-cyclodextrin to these arrays leads to their disassembly as evidenced by changes in extinction, circular dichroism, and resonance light scattering spectra. The structure or flexibility of the polymer template has an effect on the rate of disassembly; the reaction is faster on a poly(dG-dC)(2) surface than on ct DNA. The kinetic profiles for the disassembly process can be fit with great precision with a two-kinetic parameter equation in which the rate constant is itself a function of time. The reaction rate, studied in the presence of excess beta-CD, shows a dependence on the mode of detection. A model is presented to account for these observations in which the arrays become increasingly reactive with time due to beta-CD attack at the interior of the porphyrin assemblies as well as the ends.     

Supramolecular chirality transfer to large random aggregates of porphyrins

Chirality is rapidly induced in a fractal aggregate of the porphyrin t-CuPagg by addition of α-helical poly-glutamate. These results demonstrate a facile transfer of chirality via noncovalent interactions to preformed supramolecular assemblies grown in the absence of a chiral template.     

Temperature dependence of C3(X1Σg+) reactions with alkenes and alkynes, 295-610 K

C₃ reaction rates with ethene, acetylene and various of their alkyl-substituted derivatives are measured in the temperature range 295–610 K. Reactions with ethene and acetylene have 6–8 kcal/mol activation energies which become negative for the multiply alkyl-substituted species. The reaction chemistry of C₃ is compared with similar species and we conclude that the mechanism involves electrophilic addition at the carbon-carbon multiple bond. Reaction rates are apparently pressure independent over the range of 5–100 Torr.     

An EOQ Model with Substitutions Between Products

In this paper, we present an economic order quantity (EOQ) model when two products are required, and one can be substituted for the other, if necessary, at a given unit cost. We consider three cases: (i) when there is no substitution between the products, (ii) when there is full substitution between the products, and (iii) when there is partial substitution between the products. In a deterministic setting with proportional substitution costs, we would expect to find full substitution or no substitution being optimal, depending on the cost parameters. However, we observe that full substitution is never optimal; only partial substitution or no substitution may be optimal. This result can best be explained due to the non-linearity of the decision variables in the total cost expression. Finally, we present an algorithm to compute the optimal order quantities.     

CH3O(X̄ 2E) production from 266 nm photolysis of methyl nitrite and reaction with NO

The CH₃O(X? ²E) radical produced by the 266 nm photolysis of CH₃ONO is characterized by laser induced fluorescence. Using a flowing gas cell the reaction rate of CH₃O(X? ²E) with NO is measured to be (2.08 ± 0.12) × 10^?11 cm³ s^?1 based upon disappearance of CH₃O and appearance of HNO detected by laser induced fluorescence. Upper limits for CH₃O reactions with CH₄, CO, N₂O, NH₃, CH₃OH, (CH₃)₃CH and CH₂CHCH₂CH₃ are reported. These reactions are all too slow to measure under our experimental conditions.